The invention relates to a method and device for producing motor vehicle chassis parts which can be subjected to tensile stress, compressive stress and torsion and the mechanical strength of which can be adjusted over the respective cross-section, and which furthermore have high ductility and temperature stability and are made of an AlSiZnMg alloy, by means of permanent mould casting.
It is known to make highly stressed motor vehicle chassis parts from artificially ageing alloys by means of gravity casting or low-pressure casting. The artificially ageing alloys include, for example, G-AlSi12, G-AlSi10Mg, G-AlSi5Mg, G-Al3Si as well as copper-containing alloys which may additionally contain titanium, magnesium, nickel, or nickel and magnesium.
Heat treatment is dependent on the respective alloy. G-AlSi10Mg, for example, is solution heat treated at 520 to 530° C. and, after a solution treatment time of 3 to 5 hours, it is quenched in water of 20° C. Artificial ageing takes place at temperatures between 160 and 165° C. for 8 to 10 hours. Exact data for the respective alloys relating to the heat treatment of castings can be found in chapter 7.8, pages 429 ff. of Aluminiumtaschenbuch, 14th edition.
The multistage heat treatment which needs to be performed following the casting process is costly in terms of time and money. The success of the heat treatment is dependent on the exact adherence to the treatment specifications, and the annealing furnaces used in each case must permit only a very small spatial variation in temperature. As the conditions for age-hardening always apply to the complete component part, its micro-structure cannot be optimally adapted to the stress to which the chassis parts are subjected, which stress varies over the cross-section. Normally, the following minimum values in respect of mechanical strength must be achieved:    yield strength greater than 160 MPa and strain A greater than 5%.